Design of dual peak star shaped metamaterial absorber for S and C band sensing applications 

Abstract

This paper presents the detailed design configuration and investigation of a small-scale dual-band metamaterial absorber (MTMA) for solid and liquid sensing applications. The overall dimension of the MTMA unit cell is 10 × 10 × 1.57 mm³ and constitutes an affordable FR-4 substrate. The absorber exhibits dual absorption peaks at 3.470 GHz for the S-band and 7.219 GHz for the C-band, respectively. Both absorption characteristics have been validated through comprehensive simulation and experimental procedures. The dual-band absorption rate exceeded 99% during simulations, and experimental validation showed an absorption rate above 98%. For sensing applications, various solid materials, including different Rogers substrates ( RT 5880, RT 5870, RT 4003 and RT 4835) and liquids such as sunflower and crown oil, were utilized. Our findings indicate that the proposed MTMA achieves a maximum Q-factor of 191 and a sensitivity of up to 2.5 for both solid and liquid sensing applications compared to previous studies. The simulation and experimental validation of the result indicate that suggested MTMA can be effectively used in different sensing applications such as the medical and communications industry.

Introduction

Metamaterials (MTMs) are artificially created materials with extraordinary properties uncommon in organic materials¹. The composition of these materials is manipulated at the nanoscale level, enabling precise control over their behaviour and characteristics. MTMs possess a unique capability to manipulate electromagnetic waves, offering numerous possibilities for their utilization in various domains, including telecommunications^2–4, optics, sensing^5–9 and acoustics. Besides these, MTMs have exhibited exceptional potential in several fields, such as the development of cloaking devices, wave manipulation, and superlenses. As a result, this led to exciting opportunities for controlling and manipulating waves that were once unimaginable¹⁰.

A critical application of MTMs is ascertaining the adulteration of liquid and solid substances through an absorption mechanism. By incorporating MTMs into absorption-based sensors, researchers can create highly- sensitive and specific detectors for identifying impurities in liquids and solid substances. This technology can potentially revolutionize pharmaceuticals and food safety industries, where detecting even trace amounts of contaminants is crucial. With the continued advancement of MTM research, the possibilities for improving liquid chemical detection capabilities are endless. Due to sensitivity and specificity constraints, existing sensor technologies, like spectroscopy and chromatography, have certain limitations in their ability to accurately detect liquid chemical adulteration and impurities in solids substances. MTMs provide an optimistic solution to these challenges as they enable the creation of MTM absorption-based sensors capable of detecting the slightest traces of impurities in liquid and solid substances. MTMs have the potential to significantly enhance the precision and effectiveness of liquid chemical detection processes in diverse industries by surpassing the constraints of conventional sensor technologies. Researchers are making significant advancements in MTMA, which leads to new techniques for determining adulteration in various liquid chemicals and solid substances.

In previous literature, researchers have proposed and studied a range of split-ring resonators (SRR)^11–17 and complementary split-ring resonators (CSRR)^18–25 for sensing applications. SRRs and CSRRs are extensively employed in MTMA design applications due to their precision and sensitivity capabilities^26,27. Furthermore, they provide excellent miniaturization capabilities by facilitating a shift in the resonant frequency²⁸. A microwave sensor that utilizes CSRR structure for the characterization of different liquids in microwave frequencies was presented by S. Mosbah et al.²². The design incorporates a MTM CSRR in a two-port microstrip-fed rectangular patch resonator. The configuration of CSRR was constructed on Roger RO3035 Substrate, with dimensions 20×28 mm². An investigation was conducted by H. Singh et al. in²⁹ on a spanner resonator to analyze the sensing capabilities of an ultrathin MTMA for refractive index detection in biomedical samples. This design aims to enhance the output variation, sensitivity, and linearity for biomedical applications, achieving a quality factor of 19.57.

A refractive index (RI) sensor utilizing triple-band absorption in the terahertz spectrum was developed by Nickpay et al. for biosensing applications³⁰. The sensor uses graphene split-ring and patch resonators to localize the incident electromagnetic field. The sensor achieved maximum sensitivity, 32.354 value of Q-factor, by detecting variation in RI of the sample. This article presents a tunable RF sensor for measuring dielectric materials using a MTM resonator³¹. The sensor can be adjusted in both L-band and S-band. The sensor has been simulated and fabricated to evaluate dielectric characteristics in various applications. For glucose monitoring in the blood³², a non-invasive method based on a multi-parallel CSRR absorber was implemented by Wenqi et al., and a three-band sensor that utilizes terahertz technology and MTMs for the diagnosis of blood cancer³³. The sensor offers a non-invasive and precise method with the goal of transforming medical diagnostics and improving patient outcomes. An octagonal close ring resonator-based dumbbell-shaped tuning fork perfect MTMA for C- and Ku-band applications was discussed in³⁴. The design configuration of the dumbbell consists of an octagonal ring with two metal strips shaped like a tuning fork close to a ring resonator.

Cinar et al. presented a rectangular SRR MTMA to identify the solid and liquid substances within the frequency range of 2–4 GHz³⁵ and Bagci et al. implemented a dual-band meander line design configuration of MTM sensor to measure the dielectric constant of ethanol-methanol mixtures³⁶. In reference³⁷, an integrated dual T-shaped structure on a circular resonator built on a silicon substrate is presented. The resonator has a radius of 7 mm and achieves a maximum absorption of around 98%. Simulation results for radar and communications applications confirm the validity of the absorber. Rabbani et al. implemented a MTMA using asymmetric square split rings like an E-shape resonator³⁸ and by periodic arrangements of metallic square spirals, an ultra-thin and ultra-wideband characteristics MTMA was implemented by Araújo et al. in reference³⁹. A novel MTMA design with an octagonal close-ring resonator and dumbbell-shaped tuning forks for C- and Ku-band applications⁴⁰. A tri-band MTMA for advanced sensing applications, demonstrating significant absorption and sensitivity across multiple frequencies, with excellent reflection coefficients for sensing the application of liquid⁴¹. A Yagi-Uda-shaped MTMA for the microwave regime, focusing on X-band and Ku-band, is presented in⁴². The absorber has near-unity absorption peaks and significant polarization controllability. However, there is a slight discrepancy between simulated and measured results due to electromagnetic leakage and fabrication inaccuracies. An ultra-thin, polarization-insensitive, wide-angle triple-band MTM absorber (TMMA) for X-band applications is present in⁴³. It uses a composite resonator and FR-4 epoxy resin dielectric layer. Despite challenges in manufacturing and sensitivity, TMMA’s robust performance makes it ideal for broadcasting, communications, meteorology, and earth observation satellites.

One significant disadvantage of research on MTMA as sensing application has relatively low-quality factors. Furthermore, there is a lack of research in improving the sensitivity of these MTMA while maintaining their small size, as most high-sensitivity designs tend to be larger. The latest research on MTMA for sensing applications has primarily focused on either liquid sensing or solid substance sensing. This limitation hinders their capability to differentiate between closely similar compounds. This work introduces a compact star-shaped MTMA designed for dual-band solid and liquid sensing. The MTMA demonstrates high sensitivity and quality factors, validated through simulations and experiments, making it suitable for applications in medical diagnostics and communications. The proposed MTMA resolves these concerns by attaining a greater quality factor and enhanced sensitivity, all while retaining a compact size. Consequently, it outperforms existing devices in terms of performance.

Detailed layout and design configuration

Figure 1a illustrates the proposed MTMA-based sensor, while Fig. 1(b) presents the design with its corresponding boundary conditions, which are obtained through computer simulation technology software. Several structural models were formulated for the design layout, as shown in Fig. 2. The proposed design layout consists of a dielectric substrate FR-4 between two Copper (Cu) layers. The thickness of the annealed copper layers is 0.035 mm, with an electrical conductivity of 5.8 × 10⁷S/m. The substrate thickness was set at 1.57 mm. The optimal design configuration of our sensor played a critical role in achieving three distinct resonance points, resulting in enhanced sensitivity and quality factors for precise identification of adulteration in various solid and liquid substances. The dimensions of optimized parameters for the proposed MTMA are presented in Table 1.

Fig. 11.

(a) Experimental setup for measuring absorption rate for different fuels (b) measuring absorption rate for different fuels in S-band (c) measuring absorption rate for different fuels in C-band.

Fig. 2.

The reflection characteristics of the design configurations, model 1(a), model 2 (b) and model 3 (c).

Table 1.

Dimensions of corresponding parameters (all in mm).

L1	L2	L3	L4	L5	L6	L7	G1
10	10	9.60	4.245	1.76	1.76	8.49	2.60

Achieving multiple resonance points during design configuration proves its effectiveness, leading to improved sensitivity and consistent performance. This advancement greatly enhances the ability to detect adulteration and improves the overall quality of product outcomes. The required MTM start shape is enclosed in a square unit cell, which is constructed with the help of a commercial electromagnetic solution based on the full-wave finite integration technique (FIT). This was done to achieve the desired result. As a result of the high efficiency of the CST microwave studio, it is possible to extract MTM features by considering many boundary conditions such as free space, perfect electric conditions (PEC), periodic conditions and perfect magnetic conditions (PMC), and unit cells. These boundary conditions include PEC and PMC, as depicted in Fig. 1b. For the purpose of acquiring the most optimal design parameters, PEC/PEC is utilized in the x/y directions, and while in the z-direction, we apply an open space boundary. Figure 1b visually represents the boundary conditions for the proposed operation.

Fig. 1.

(a) Showcases the proposed structural design of a MTMA, while (b) presents the design with its corresponding boundary conditions.

Three simulations were conducted to examine the impacts of SRR and star-shaped resonators. The subsequent sections provide a detailed account of the outcomes, excluding the sensor layer. Figure 2a depicts the evaluated proposed design with a single square SRR (model 1). A single resonance frequency (RF) with a magnitude of -15 dB has been observed to have taken place at about 10.29 GHz, as seen in the figure and observed. Figure 2b displays the evaluation of the proposed design with a single square SRR (model 2) and its impact on reflection coefficient parameters. Two RFs are observed in the model 2 configuration, measuring 4.260 GHz and 10.85 GHz, with magnitude values of −37.58 dB and − 25.52 dB. This increase in reflection value, when compared to model 1, can be attributed to this factor. Model 3’s reflection coefficient is depicted in Fig. 2c. The model consists of a square SRR and a star-shaped figure. The third model is crucial in generating a high reflection coefficient value at two resonance peaks, approximately at 3.470 GHz and 7.219 GHz, as depicted in Fig. 2c. Therefore, the tuning process allows us to create resonances and thereby increase the reflection coefficient values by appropriately designing and positioning resonators.

Analysis of the impact of metal and substrate

It is essential to thoroughly analyze the influence of metal and substrate on MTMA in order to maximize their performance. Various factors can influence metals’ resonant frequency and electromagnetic properties, while substrates play a crucial role in ensuring mechanical stability and seamless integration into devices. Having a clear understanding of these impacts helps us during design decisions, ultimately improving the efficiency and functionality of MTMA. This analysis helps customize MTMA for specific applications, ranging from communications to sensing, to ensure the best possible performance and reliability.

Figure 3a demonstrates a range of substrates, including ArlonD 410, Roger 5880, Roger 4350, and FR-4. These substrates were used in the simulation to examine their impact. According to the Eq. (1) for resonance frequency mentioned in reference⁴⁴.

1

Fig. 3.

The recommended design’s reflection coefficient under varied (a) substrate material and (b) resonator material.

Inversely proportional to the capacitance (C), the RF is inversely proportional to the capacitance. This indicates that the value of C drops as the RF increases. Due to the fact that the value of the C increases as the dielectric constant increases (, the RF tends to decrease in accordance with Eq. (1), as demonstrated in Fig. 3a. The dielectric constant values for the different substrates are as follows: 4.3 for FR-4, 4.1 for ArlonD 410, 3.66 for Roger 5880, and 2.2 for Roger 4350. These values are based on the material library that is included in the CST software. Figure 3b illustrates the influence of resonance materials on the reflection coefficient (S₁₁). It is evident that resonance materials do not affect resonance shifts compared to dielectric substrates. Nevertheless, the plasmonic resonance response influences the scattering parameter’s value.

Electromagnetic field and surface current

By comprehending the characteristics of the electromagnetic fields, we can acquire valuable knowledge about the physical properties of the electromagnetic wave within the absorber. Through the application of Maxwell’s equations, a comprehensive analysis can be conducted to examine the intricate interactions between the electric field (E-field), magnetic field (M-field), and the absorber during resonances. This analysis offers valuable insights into the absorption mechanism. In our analysis, we will discuss the behaviour of the E-field and the H-field on both the patch and the substrate. However, we will now discuss the distribution of the patch. The electromagnetic field values at each point of the MTM cell are determined by applying Helmholtz’s equations⁴⁵.

2

Where k is a propagation constant and is written as, where ℇ^* is the effective permittivity of the MTM.

3

4

By simulating Eq. (2) with the value of k, we get the electric field Eq. (5) and magnetic field Eq. (6).

5

6

Figure 4a, b, c and d depict the distribution of E-field and H-field for the proposed MTMA design at the two RF of 3.47 GHz and 7.219 GHz. From Fig. 4a, b, we observed that at the top side, the left side of the square, and the surrounding side of the star shape, the E-field is higher than the central shape of the start. At the same time, the H-field distribution is higher on the right upper corner and left low corner than on the left upper and lower right corner.

Fig. 4.

The field distributions of the proposed MTM structure are depicted (a,b) E-Field at 3.47 GHz and 7.219 GHz (c,d) H-field at 3.47 GHz and 7.219 GHz.

Meanwhile, the surface current distribution is clockwise at both RFs, as depicted in Fig. 5a, b. From the figure of H-field distribution and surface current distribution, It is evident that the surface current flows in a clockwise direction at RFs, resulting in alignment with the incident H-field.

Fig. 5.

Current distributions of the proposed MTM structure are depicted (a,b) surface Current at 3.47 GHz and 7.219 GHz.

Result and discussion

The simulations were conducted using computer simulation technology (CST.) Microwave Studio commercial software utilizes a frequency domain solver and finite element analysis. The unit cell’s boundary condition is used to simulate the PEC and PMC boundary structure in the x- and y-directions, while an open-space boundary is employed in the z-direction. Figure 1(b) illustrates the simulation setup where the electromagnetic propagation vector is perpendicular to the cross-section of the MTMA structure, specifically along the z-direction. The electric field is oriented in the y-direction, while the magnetic field is oriented in the x-direction. The scattering parameters in two dimensions are obtained using CST software to calculate the absorption spectrum that varies with frequency^44,46.

7

In Eq. (7) R(ω) represents the |S₁₁|, also represented by |S₁₁|. Similarly, T(ω) represents the transmission coefficient, also represented by |S₂₁|. The copper layer completely covers the back side of the substrate, effectively blocking any waves from passing through the structure. As a result, T(ω) = 0. Therefore, perfect absorption is achieved when there is no reflection.

MTMA as a sensor for solid materials

The absorption characteristics of MTM structures can be utilized for sensing applications involving both solid and liquid materials. This capability opens opportunities for developing advanced sensors that can accurately detect and analyze various substances based on their absorption properties. Such sensors could have wide-ranging applications in environmental monitoring, medical diagnostics, and industrial process control. MTMA can also detect properties such as permittivity, refractive indices, and temperature. In this study, we applied the proposed MMA specifically for sensing solid materials. The proposed model involves placing the substrate layer on top of MMA, ensuring direct contact with both FR-4 and the FS-SRR. The detection mechanism of the proposed model relies on shifts in RF, which manifest as changes in the absorption peaks from their resonant positions. Equation (8) explains the process of determining the RF for each absorption peak in MTMA, which is based on capacitance and inductance⁴⁷.

8

The capacitance and inductance in this context are affected by the topology and dimensions of the MTMA structure. When a material or sample is placed onto the MTMA structure, the capacitance of the test material (CMUT) combines with the capacitance of the MTM itself (CMTM). The capacitance increase caused by the MUT results in a shift in the resonance frequency, which can be represented in Eq. (9)⁴⁷.

9

Since the area and distance are predefined based on the topology and dimensions of the MTM, the CMUT relies solely on the permittivity of the MUT. The change in resonance frequency due to the loading material is described by Eq. (10) ⁴⁷.

10

Simulation validation of an absorber

Figure 6a illustrates the MTMA model employed for sensing in our study. Figure 6a depicts the uppermost material as a substrate with varying permittivity, commonly referred to as the material under test (MUT). Following the initiation of MUT, a copper metal patch is utilized to shape the patch. A patch is applied on the FR-4 substrate, with the back side of the FR-4 covered with copper to prevent signal transmission, resulting in zero transmission. We selected four materials with varying permittivities (ranging from 2.17 to 3.55) while maintaining a consistent thickness of 1.2 mm. The MUT are Rogger RT 5880 (), Rogger RT 5870 (), Rogger RT 4003 () and Rogger RT 4835 (). Figure 7 showcases the sensing characteristics of the proposed model, utilizing the newly designed absorber. The MTMA effectively absorbs electromagnetic waves in both the S and C-bands, exhibiting consistent absorption across multiple resonances of the detection materials. As illustrated in Fig. 6c, d, the resonances associated with the absorption rates shift to lower frequencies due to their inverse relationship with the dielectric constants.

Fig. 6.

(a) Solid material sensing model based on MTMA (b) absorption rates of different Rogers substrates (c, d) frequency shift for the lower band and upper band.

Fig. 7.

(a) Liquid sensing model based on MTMA (b) absorption rates of different liquids (c,d) frequency shift for the lower band and upper band.

Figure 6b, c, d illustrates the sensing characteristics of the proposed absorber based on a MTM unit cell. The proposed unit cell based on MTMA can be used for sensing applications in both bands due to its distinct resonance points. Figure 6b illustrates the changes in resonance points for both bands. As depicted in Fig. 6b, the placement of various materials on the unit cell results in a noticeable shift in the resonance point toward a lower position. Figure 7c, d illustrate an enlarged view of the changes in resonance points for both bands. When various materials were applied to the unit cell, RF shift was observed in absorption. This can be attributed to resonances being inversely related to the dielectric constants.

Sensing applications for liquid

Due to their exceptional absorption characteristics, MTM-based unit cells can be effectively utilized for sensing applications. The MTMA working principle depends on the resonance frequency shift, which happens when we load liquid in the sample holder. Changes in the testing material’s properties within the RF and microwave frequency range result in a variation in the overall C of the MTM structure, which subsequently shifts the RF, which can be explained through Eq. (8). The sensing application is conducted in a similar way to how it is performed for solid materials. We use a sample holder to carefully fill it with the liquid sample placed on the unit cell. The setup for the suggested MTMA is shown in Fig. 7, demonstrating a comprehensive sensing investigation. Figure 7a illustrates the scenario of loading testing liquid onto the proposed MTMA. Four different liquid carbohydrates have been selected for testing: kerosene, octane, diesel, and petroleum. Each of these liquids has a specific dielectric constant value, with kerosene having a value of 1.80, octane at 1.960, diesel at 2.10, and petroleum at 2.20. Figure 7b displays the absorption characteristics plot for the liquid testing. Figure 7c, d presents a zoom overview of the absorption for the S and C bands. Figure 7b illustrates a noticeable change in RF in liquid sensing applications. This change occurs because of the inverse correlation between the frequency and the permittivity of the tested liquid. The enlarged view for both bands is depicted in Fig. 7c, d.

Experimental validation of absorber

This section provides a comprehensive overview of the experimental setup, including the fabrication procedure. We also demonstrate the performance of the proposed MTMA through experimental results. Once we have finalized the design in CST, we proceed to import the .dx file of the design. Our fabrication process utilizes the LPKF ProtoMat PCB Milling Machines for precise and efficient results. The experimental setup includes a Vector Network Analyzer (VNA), a unit cell, and waveguide ports for S-band and C-band frequencies. We utilized a VNA to accurately determine scattering parameters, including reflection and transmission. Before commencing the experimental process to minimize errors, we calibrated the VNA using a kit for two different frequency bands separately. Figure 8 illustrates the complete experimental setup configuration.

Fig. 8.

Experimental setup for measurement scattering parameters.

Sensing of solid materials and liquid substances

As previously stated, the back side of the MTMA unit cell is coated with copper, resulting in the reflection of all waves and preventing any transmission. The measured absorption for the MTMA is depicted in Fig. 9 during the experiment setup through scattering parameters. The enlarged view of each band is also depicted in a separate figure. Based on the graphical representation of the simulated (Fig. 6b) and measured absorption Fig. 9, it is clear that our proposed unit cell performs exceptionally well. Once the reflection coefficient of the proposed unit cell has been measured, we proceed to test it on four different substrate materials: RT4835, RT4003, RT5880, and RT5870. These substrates have been precisely cut to match the size of the unit cell. Next, we place these substrates on top of the MTMA unit cell and accurately measure the reflection coefficient to calculate the absorption. Form this expression , it is clear that RF is inversely proportional to the dielectric constant’s square root. If the material’s dielectric constant increases, the RF decreases, and if the dielectric constant decreases, the RF increases.

Fig. 9.

Measured absorption of MTMA unit cell.

The sensing characteristics of the proposed unit cell model based on an absorber for different solid materials are depicted in Fig. 10a, b for both bands. It is evident from Fig. 10 that the proposed unit cell absorber consistently absorbs in both the S- and C-band for various materials. Figure 10a, b clearly demonstrate a noticeable change in RF for both bands. It is evident from Fig. 10 that the absorption of the material shifts to lower frequencies as the dielectric constant increases. This is due to the inverse relationship between frequency and dielectric constant. Equation (10) can be utilized to extract the sensitivities from these characteristics⁴⁴. A short comparison for simulation and measured sensitivity and Q-factor for different solid materials and liquid substances in the S-band is illustrated in Tables 2 and 3.

Fig. 10.

(a) Measured absorption rate for different different substrates in S-band (b) measured absorption rate for different substrates in C-band.

Table 2.

Simulated and measured value of sensitivity and Q-factor for solid material.

Material name	Sensitivity value		Q-factor value
	Simulated	Measured	Simulated	Measured
RT5870	1.4	1.2	96	87
RT5880	1.5	1.4	92	76
RT4003	2.8	2.5	198	191
RT4835	2	1.8	50.9	47.7

Table 3.

Simulated and measured value of sensitivity and Q-factor for liquid chemical.

Material name	Sensitivity value		Q-factor value
	Simulated	Measured	Simulated	Measured
Kerosene oil	0.17	0.18	14	7.9
Octane	0.096	0.017	14.3	8
Disesel	0.09	0.05	14.4	6.65
Petroleum	0.014	0.019	15	7

Figure 11 illustrates the experimental setup for liquid sensing applications and the absorption rate obtained from the experiment. Figure 11a illustrates the entire experiment setup. The sample holder is securely positioned on the top of the unit cell and filled with liquid. We use a syringe to carefully fill the sample holder with liquid. Next, we made adjustments between the waveguide ports and proceeded to measure the reflection coefficients. Figure 11b, c illustrates the absorption rates of various fuels in both the lower and upper bands.

Q-factor and sensitivity analysis

The effectiveness of the MTMA-based sensor for practical applications is determined by its performance metrics, particularly sensitivity and quality factors. When considering MTMA for sensing applications, it is crucial to evaluate these metrics to determine the sensor’s ability to accurately detect and differentiate environmental changes or variations in material properties. The term sensitivity in the context of MTMA-based sensors refers to their ability to detect changes in the surroundings environment or the specific properties under observation. An analysis was conducted to quantify the performance metrics of our sensor, which is based on a MTMA. These objectives are achieved by examining the shift in RF that takes place due to variations in the dielectric properties of materials under test, such as solid and liquid⁴⁴ as given in Eq. (11).

11

The Q-factor determines the sharpness of the resonant peak in MTMA-based sensor, which is strongly correlated with the decay rate of the oscillation and bandwidth. When the value of the Q-factor is higher, then bandwidth decreases at resonance, which boosts the sensitivity of the sensor. In this study, we observed a continual drop in the Q-factor as permittivity changes, suggesting an expansion of the resonance peak. This broadening may reflect material properties shifts, affecting the sensor’s operational capability. The quality factor is calculated by following the Eq. (12)⁴.

12

By examining the performance metric sensitivity and quality factor, then it is possible to understand sensor performance thoroughly. If the sensitivity value of a sensor is high, then a higher value ensures that the sensor can detect a slight variation in material under test. Additionally, a higher Q-factor value allows for precise signal processing at the RF. The data from the latest research, presented in Table 4, provides strong evidence for the strength and versatility of the proposed MTMA sensor. Table 4 clearly demonstrates the superior performance and cost-effectiveness of the proposed MTMA-based sensor across various applications, ensuring reliable and accurate measurements.

Table 4.

Comparisons of proposed sensor design with reported studies in recent.

Ref.			Frequency range (GHz)	Unit cell dimensions (mm)	Substrate material	Maximum Q-factor	Maximum sensitivity	Maximum absorption	Application
29	(Singh et al., 2022)		85–110		FR-4	19.57	1.41	99%	Biomedical pplication
34	(Rabbani, et al., 2024)		2–18		FR-4	51.90	Not mentioned	96%	Absorber for liquid sensing applications
35	(Cinar & Basaran, 2024)		2-3.5		Polylactic Acid	Not mentioned	1.17	98%	characterization of liquid and solid
37	(Bennaoum et al., 2023)		5–15		Silicon	Not mentioned	Not mentioned	99%	RADAR and Sensors systems
38	(Rabbani, et al., 2024)		2–12		FR-4	58.3	0.89	98.45%	Liquid Sensing applications
40	(Afsar et al., 2022)		4–18		FR-4	Not mentioned	Not mentioned	99.15%	Stealth-coating application
41	(Zikrul Bari Chowdhury et al., 2024)		2–14		FR-4	150	1.56	99.9%	Liquid sensing applications
42	(Bilal et al., 2022)		10–16		FR-4	Not mentioned	Not mentioned	99%	Airborne radar applications
43	(Ji et al., 2021)		6–18		FR-4	Not mentioned	Not mentioned	99%	Meteorology and satellites application
Proposed work			3–8		FR-4	191	2.5	99.8%	Absorber for liquid and solid sensing applications

Comparative with prior research

Compared to earlier research work, the proposed MTMA for liquid and solid sensing applications presents notable achievements in multiple parameters. The suggested MTMA operates in S-band and C-band frequency ranges, with compact dimensions as compared to other studies, and constitutes an FR-4 substrate frequently used in prior research. The proposed MTMA achieves a maximum Q-factor of 191 compared to the previously reported study⁴¹. Furthermore, the proposed MTMA demonstrates a maximum value of sensitivity, which is higher than the 1.56 and 1.41 sensitivity reported in^29,41. The sensor’s application as an absorber for liquid and solid sensing is in line with other applications reported in previous works, such as liquid sensing in^34,38, and⁴¹, biomedical applications in²⁹, and RADAR and sensor systems in³⁷. The proposed sensor exhibits an enhanced Q-factor and sensitivity, along with a competitive absorption rate. This highlights its potential for superior performance in its intended applications, showcasing notable advancements compared to existing designs in the literature.

Conclusion

We present a compact star-shaped dual-band MTMA crafted for high-end sensing applications, demonstrating impressive electromagnetic absorption and sensitivity at multiple frequencies, particularly at resonant frequencies of 3.26 GHz and 7.25 GHz. The MTMA, fabricated using an economical FR-4 substrate, operates effectively within the S-band and C-band frequencies, achieving absorption rates above 99% during simulations and over 97% during experimental validation across different solid and liquid materials. The dual absorption peaks provide high sensitivity and a superior quality factor, reaching a maximum of 191, which outperforms previous studies. This enhanced sensitivity makes it suitable for diverse sensing applications, including medical, communications, and industrial sectors. The performance and dimensions of the absorber are compared with the other ones presented in the literature, highlighting the proposed structure’s excellent capacity. This research highlights the practicality and efficiency of the proposed MTMA, offering a viable solution for modern sensing requirements in diverse applications. Future studies can enhance MTMA design for better quality and sensitivity, and expand its frequency range for broader applications in medical, environmental, and communication fields.

Author contributions

MAK: Conceptualization, methodology, investigation, validation, writing—original draft. WHY: Supervise, fund acquisition, project administration, and software. A. H.: Writing—original draft, supervision, validation, formal analysis, M. S. I.: Investigation, writing-review & editing, validation. N.U.:Data curation, validation. MTI: Administration, resources, Visualization, data curation, HHG: Validation, writing-review & editing. LYC: Investigation, writing-review & editing. MSS: Visualization, data curation, validation. TAK: Formal analysis, Data curation.

Data availability

The corresponding author oversees the data set, which is available upon request.

Declarations

Competing interests

The authors declare no competing interests.